Electrical Transformer tutorials Current Potential and Auto tutorials

Current Transformers The primary of this transformer consists of a few turns or even a single turn to carry the current to be measured and is connected in series with the main circuit. The secondary winding with large number of turns supplies a reduced current to the ammeter. The meter scale is calibrated directly in terms of the primary circuit current.The core is worked at low flux density so that, at all loads, secondary current is a constant ratio of the main circuit current. When the cuurent is flowing in the primary circuit, the secondary circuit should not be opened. In that case high voltage may be induced in the secondary and the core may become over saturated, heated up and thereby damage the magnetic properties permanently.

Potential Transformer
This is used to reduce the primary voltage to a safe value for operation of voltmeter and other instrument. Primary is connected to the H.T. to be measured and the secondary to a voltmeter. It is so designed that the ratio of primary to secondary is constant throughout. To limit the short circuit in case of failure of the transformer, limiting resistances are placed in series with the H.T. winding.

Auto-transformer works on the priciple of self Induction
It has only one winding which performs the function of both primary and secondary winding. As in ordinary transformer, the transformation ratio in autotransformer, is also equal to the turns ratio.
In case of step down transformer, the complete winding acts as primary winding while the tapped section of this winding works as secondary winding. In the step up transformer, the whole winding works as secondary winding and its there is much saving of copper. These transformers are used as regulating transformers where only a small variation of voltage is required. It is mainly used for starting and speed control of induction motors. It suffers from a disadvantage that the two windings are not electrically separate and in case of failure of insulation between the two, either a sever shock may be felt on the low voltage side.

Various parts of a Transformer
Primary winding
Secondary winding
Oil level
Conservator
Breather
Drain cock
Tube for cooling
Transformer Oil
Earth Point
Explosion vent
Buchhol's Relay
H.T. Terminals
L.T Terminals


Free Pdf file about the kinds of Transformer

Current Transformers
Current transformers are used in electrical grids for measurement and protective applications to provide signals to equipment such as meters and protective relays by stepping down the current of that system to measurable values.

Instrument Transformers
Technical Information and Application Guide

Selecting Current Transformers
As engineers, we are aware that electrical power systems have grown. How much have they grown?

Current Transformer Principles and Operation
Used with watt transducers enable the owner to control demand as well as monitor building and/or tenant power consumption. When CT's are used with Current Transducers, the result is an excellent method of diagnosing the performance of fans,pumps, chillers.

Potential Transformer
Voltage transformers connected line-to-ground cannot be considered to be grounding transformers and must not be operated with the secondaries in closed delta because excessive currents may flow in the delta.
VOLTAGE TRANSFORMERS
Potential transformer are so small that they may be neglected for protective-relaying purposes if the burden is within the "thermal" volt-ampere rating of the transformer. This thermal volt-ampere rating corresponds to the full-load rating of a power transformer.

Auto Transformer
The currents drawn by these two windings are out of phase by 180◦. This prompted the use of a part of the primary as secondary. This is equivalent to fusing the secondary turns into primary turns.

Transformers vs. Autotransformers
A transformer converts audio from one voltage and impedance to a different voltage and impedance. Transformers are passive which means they do not require a  power supply to operate.